Device for compensating the temperature of systems for distant measurement of the number of revolutions



A, KELLER April 25, 1944.

DEVICE FOR COMPENSATING THE TEMPERATURE OF SYSTEMS FOR DISTANT MEASUREMENT OF THE NUMBER OF REVOLUTIONS Filed Oct, 23 1940 2 Shuts-Sheet 1 uumnml II llllllll Ill I'NVEN TOR RNOLD KELLER BY u ekq H ORNEY April 25, 1944. A KELLER 2,347,563

DEVICE FOR COMPENSATING THE MPERATURE OF SYSTEMS FOR ms NT 0F TART MEASUREME T NUMBER OF REVOLUTIONS Filed Oct. 25, 1940 2 Sheets-Sheet 2 INVENTOR ARNOLD KELLER 5% g H5 TTORNEY Patente d Apr. 25, 1944 DEVICE FOR COMPENSATING THE TEM- PERATURE OF SYSTEMS FOR DISTANT MEASUREMENT OF THE NUMBER OF REVOLUTIONS Arnold Keller, Berlin-Wilmersdorf, Germany; vested in the Alien Property Custodian Application October 23, 1940, Serial No. 362,402

In Germany September 15, 1939 1 Claim.

The systems for measuring the number of revolutions treated hereinafter are operated by driving a dynamo (the transmitter) with the number of revolutions to be measured and by measuring at the receiving station the voltage generated by the dynamo, mostly by means of a' direct current instrument via rectifiers or by means of an electrodynamic measuring instrument.

At higher temperatures of the transmitter the indication obtained in this way is reduced for two reasons: firstly, owing to the rising resistance of the windings in the transmitter, and furthermore owing to the reduction of the strength of the magnet, as shown by every magnet. The first mentioned influence is in most cases considerably greater than the latter. The copper resistance varies by 4% for each degrees centigrade, and the error caused thereby depends upon the proportion of this resistance variation to the total ohm resistance of the circuit. In order to make it small, it would be necessary to use a very high constant series resistance. Since the current consumption of the indicating instrument is not optionally variable, it would be necessary to make the transmitter very strong and, therefore, large and heavy, which is mostly undesirable. The temperature variation of the magnetic flux is of the order of 0.3% for each 10 degrees centrigrade, but in many cases the actually occurring error of indication, especially with large numbers of revolutions, is even of a higher order than that mentioned.

In most of the systems for distant measurement of the number of revolutions the temperature compensation of the transmitter is eifected by varying the strength of the magnet in de pendence on the temperature by magnetic shunt connection of a ring or the like consisting of an iron-nickel alloy. With increasing temperatures, a smaller number of lines of force will be shortcircuited via the iron-nickel body so that the induced voltage will rise.

This method, 1. e. use of the shunt, has two considerable disadvantages: (1) the reproduction of a certain course of the temperature is exceedingly difiicult even with small magnetic unhomogeneities of the material or with a somewhat heterogeneous magnetization, and (2) by this way of compensating the variations due to the temperature a systematic curve error arises at higher temperatures. With a limited current loading of the transmitter by the indicating instrument, a variation of the magnetic flux will have a comparatively greater eiiect upon the indication of the number of revolutions, if the number of revolutions is higher than if it is lower, because the current intensity is not proportional to the number of revolutions, but rises more slowly with greater numbers of revolutions. As a variation of the resistance of the transmitter owing to the rising temperature causes the same relative variation of the indication of the number of revolutions for all values of the number of revolutions, the result of this is that a transmitter, which is correctly compensated for average speeds, will be over-adjusted for higher speeds and under-adjusted for lower speeds.

Apparently, the most natural way of compensation wbuld be to insert a series resistance decreasing with increasing temperature in such a way that the error due to the temperature is compensated. However, the existingresistances of this kindeither have avery large or a very small negative temperature coefiicient of the electric resistance. Bodies with very large temperature coeflicients are many temperature-dependent conductors, especially metal oxides. Their temperature coefficients amount to a few per cent for each degree Centigrade. Consequently, the absolute variation of these resistances is considerably greater for lower temperatures than for higher temperatures. For example, the resistance of cuprous oxide resistances is reduced to one-half by a rise in temperature of 30 degrees centigrade, so that the dillerential variation of their resistance at, for example, 50 C. will still amount to about one-half of that at 20 C. On the other hand, the output of the transmitter will mostly not be suflicient to permit a sufficient- 1y high series resistance for the compensation of temperature by means of series resistances with small negative temperature coefiicients. Such resistances, for example certain kinds of carbon, have a temperature coefficient of a few tenths of a per cent for a temperature variation of 10 C. Since the temperature coefiicient of copper is four per cent for 10 C., the order in the case of the series resistance would have to be ten times as large as that of the copper resistance, so that the transmitters would have to be extremely large and heavy.

According to the invention, it is possible to obtain a compensation of temperature with comparatively small series resistances, using resistances with very large temperature coeflicients, by providing a series resistance in which a highly temperature-dependent conductor 3, is connected in parallel with a resistance 4, varying but slightly with the temperature. By correctly dimena ase'nscs cloning the resistances 3, 5, it is possible to obtain a practically completely lineardependence or the resistance upon the temperature. If necessary, there may also be inserted in the sys tem a small temperature-dependent series resistance 5, in order to obtain a more improved linearity. A still more improved linear or, if necessary, not linear dependence upon the temperature may be obtained by inserting (mixed series and parallel connection) additional highly or slightly temperature-dependent resistances 3, 4 respectively (not shown) so as to form a network. With this arrangement, it is generally possible to obtain'a practicaliycompletely sufficient linear compensation of temperature with a series resistance 5, which,-in total, at the lowest temperature occurring, is about double the amount by which it must be reduced when the temperature rises.

' As, apart from the influence of the copper resistance 2, also the magnet l, in the transmitter (Figs. 1 and 3) causes a reduction in the indication at higher temperatures (variation of the remanence by about 0.3% for C.) it is necessary, if an iron-nickel shunt (not shown) is to be altogether avoided, to cause a certain additional linear reduction of the total resistance, which compensates the temperature coefiicient of the magnet i. It should amount to about 0.3% for each 10 C. The result-of this is that an irregularity of the temperature compensation is caused for difizerent numbers of revolutions, being in the reverse order as in compensating the infiuence of the copper resistance 2, by means'of magnetic s'hunt (see above) and generally to a considerably smaller amount. Therefore, the transmitter is now still under-compensated for large numbers of revolutions and over-compensated for small numbers of revolutions, if it is correctly compensated for average numbers of revolutions. This still remaining error may be compensated according to the invention by the self-heating of the temperature-dependent conductor 3, as the current passes through. By a suitable heat insulation of the temperaturedependent conductor *5, this compensating efiect may be dimensioned so as to obtain a practically complete compensation of the error due to the temperature at difierent numbers of revolutions.

In order also to obtain a correct indication in locally not uniform temperatures of the transmitter, it is advisable to mount the temperature-- dependent conductor-8, as near as possible to the copper coils 2, of the transmitter, for example to insert it between two coils as shown in Fig. 1, or to wind it into one of the coils. The above mentioned optimum heat insulation may in this case be efiected by providing the resistance beforehand with a heat-insulating cover (not shown). If the heat insulation is too high, this may be relieved by providing two resistances of equal size or one resistance of larger dimensions which will then, of course, be less selfheating.

caused thereby. All considerations mentioned above also apply in this case. v

A constructional example of the object of the invention is illustrated diagrammatically in the accompanying drawings, in which:

Figs. 1 and 2 show circuit diagrams of the transmitter (Fig. 1) and -01 the indicating instrument (Fig. 2).

Fig. 3 is an axial section through the transmitter.

Fig. 4 is an interior view of the indicating instrument, and I Fig. 5 is a detail view showingjhe compensating resistance positioned, inside the insulating taping of the dynamoelectric coil windings.

In Figs. '1 and 3 or the drawings, 8 designates the revolving magnet, Z the individual coils, 8 the temperature-dependent resistance, A the temperature-independent resistance connected in parallel, and 5 the series resistance.

According to Fig. 3, the magnet i is fixed to the shaft 6 which is driven in a suitable manner from the shaft whose number of revolutions is to be determined. The magnet is rotatably mounted with ball bearings 8 in the housing I.

The coils 2 are influenced in known manner. The one end of the coils is connected to the line :12, Whereas the other end of the coils is connected on the one hand to the temperaturedependent resistance 3 (connection a) and on the other hand to the temperature-independent parallel resistance t (line b). The temperaturedependent resistance 3 is connected via the line 0 to the parallel resistance d. The series resistance 5 is connected to the line 71., From the lines a: and y the current generated by the transiron core l2 upon which is wound a field coil i8. Furthermore, there are arranged in the housing the series resistance il and the temperature-independent parallel resistance H5. The number it designates the temperature-dependent resistance. These individual parts are connected in such a manner that the current is conducted from the line a to one end of the series resistance It. The resistance l5 arranged behind the series resistance is connected in parallel with the temperature-dependent resistance it via the lines at and e. The coil ii and the field coil I3 are connected in series and have a connection via the "line I with the line 1.

What is claimed is:

In an electrical generating and transmitting system having means for compensating for tem: perature variations, 9. dynamoelectric machine having a magnetic circuit of magnetic material and tape insulated conductive windings, a transmission circuit in series with said windings, two resistances in series with said circuit and windings and in parallel with one another, one of said resistances having a high negative temperature coefiicient and being located within the insulating taping of the windings and the other resistance having a low temperature coefilcient.

ARNOLD KEILER. 

